docs: def load_to_array(self, keys):
          """
          This loads the data contained in the catalogue into a numpy array. The
          method works only for float data
  
          :param keys:
              A list of keys to be uploaded into the array
          :type list:
          """
          # Preallocate the numpy array
          data = np.empty((len(self.data[keys[0]]), len(keys)))
          for i in range(0, len(self.data[keys[0]])):
              for j, key in enumerate(keys):
                  data[i, j] = self.data[key][i]
          return data